1. Field of the Invention
The present invention relates to a paper-making machine, and, more particularly, to a heat exchanger used to cool process liquid for use in a paper-making machine.
2. Description of the Related Art
A paper-making machine uses a plurality of different liquids during the paper-making process. Such liquids, i.e., process liquids, are used for example to make the fiber material web, and lubricate and/or cool certain mechanical components within the paper-making machine. The process liquid may be in the form of oil, condensate, ethylene glycol, etc. used to cool and/or lubricate various mechanical components within the paper-making machine. For example, the paper-making machine includes a plurality of rotatable rolls and cylinders which are carried at each longitudinal end thereof by associated bearing assemblies. Since the peripheral velocity of the rolls or cylinders may approach 6000 feet per minute and the rolls or cylinders may weigh several tons or more, it may be desirable to lubricate the bearing assemblies which carry the rolls or cylinders with a lubricating and cooling liquid.
Moreover, the process liquid may be considered as the fiber suspension which is being processed into a fiber material web within the paper-making machine. It is typically desirable to maintain the fiber suspension at an elevated temperature such that the water within the fiber suspension may be more easily transformed to a gas (i.e., steam) and thereby be removed from the fiber material web. However, it may be desirable for certain applications to decrease the operating temperature of the fiber suspension by cooling the fiber suspension.
It is known to cool a process liquid used in a paper-making machine by transporting the process liquid through a pipe which is submersed within a source of cooling water. For example, paper-making machines are commonly placed adjacent to a river which is used as a source of electrical and mechanical power, and may also be used to transport the wood logs consumed during the paper-making process. A long, metal pipe may be submersed within the river water. The process liquid is transported through the pipe and heat from the process liquid is transferred through the thermally conducting metal pipe into the lower temperature river water.
A problem with cooling the process liquid in a manner as described above is that a possibility of contamination of the river water by the process liquid exists. The metal wall of the pipe acts as an effective thermal conductor to transfer heat from the process liquid to the river water. However, the metal pipe may become damaged from mechanical impact and/or corrosion. The damaged pipe may allow the process liquid to flow into the river water, thereby contaminating the river water. Governmental fines and cleanup costs associated with such contamination may be expensive. Furthermore, loss of the process liquid in the paper-making machine may necessitate the replenishment of the process liquid, thereby also resulting in increased additional cost.
What is needed in the art is a heat exchanger for cooling a process liquid used in a paper-making machine using a source of cooling water, which adequately transfers the heat from the process liquid to the cooling water and also reduces the possibility of environmental contamination of the cooling water by the process liquid.